1. Field of the Invention
The present invention relates to a recording material, and in particular, to a recording material on which an image can be recorded by a thermal head or the like.
2. Description of the Related Art
Recording materials on which an image is recorded by heat being applied thereto by a thermal head or the like have come into wide use in recent years as the recording devices therefor are simple, reliable and do not require maintenance. Such recording materials include, on a support, a recording layer which contains, as color forming components, an electron donating dye precursor and an electron receiving compound, or a diazo compound and a coupler, for example. An image is recorded by utilizing a color forming reaction of the color-forming components which proceeds due to the application of heat.
In such a heat-sensitive type recording method, an image is recorded due to the application of heat. Thus, the surface temperature of the recording material becomes high during image recording. Further, if a contact type recording means such as a thermal head is used, pressure is applied to the recording material during the image recording. At this time, moisture and air in a recording layer expand due to the heat applied thereto, and then move to the surface of a coating layer of the support, and when the moisture and air reach the coating layer and continue to expand thereon, they form air gaps and cause a so-called blistering. The generation of blistering causes a deterioration of image quality such as glossiness, of a recorded image.
As a method of suppressing the generation of the blistering, a method is known in which a layer having low permeation with respect to gas water vapor, e.g., a so-called undercoat layer, is formed between the recording layer and the support. As the undercoat layer, a layer that contains a water-soluble resin such as polyvinyl alcohol, as a binder, is preferably used. Further, if the undercoat layer containing therein the polyvinyl alcohol is formed on a support, the coating layer is leveled to form a flat surface after being coated. Therefore, it is preferable to use a method in which, first, polyvinyl alcohol is dissolved in water, then methanol or the like is added to the mixed solution of the polyvinyl alcohol and the water, to thereby prepare a coating solution for undercoat layer.
However, even in a case of the undercoat layer containing the polyvinyl alcohol as described above, there is a possibility that cracks will be produced due to physical stress, and gas water vapor will reach the support via the cracks, whereby blistering might occur.
As described above, the recording material comprises a recording layer on a support. However, when the recording material is immersed in water, the recording from the support might peel off. It is desired to provide a recording material in which water resistance and wet bond strength are improved.
The coating solution for undercoat layer has high viscosity, and at the time of forming the undercoat layer, there has been a problem regarding coating suitability when the coating solution is coated using a gravure coating method which has been considered to be preferable from the viewpoint of cost. Further, there are some cases in which, after images were printed in an atmosphere of low humidity (for example, 10% at 20° C.), fine cracks were produced on the surface of the undercoat layer.